I too use WD-40 daily in a professional setting on seriously expensive sporting equipment.
The one thing it does for me that not much else does as well OR AS CLEANLY is . . . it goes in quickly because it is thin and can be blown in there with the aerosol . . . then . . . it dissolves most all of these silly, over priced, over hyped, miraclegunks that people keep finding to squirt or spray all over their things. Usually all that stuff just sets up, dries out and causes more problems than if they just used sewing machine oil or 10wt.
Now solvent would initially do the same thing but it would be worse to breath and it would eventually evaporate entirely and the bloody thing would seize up again. The WD stays pretty thin and just keeps stuff working AND working Well !
Now I COULD disassemble the whole thing, clean everything in solvent and reassemble it with real grease or machine oil as appropriate BUT sometimes that would involve destroying some expensive parts that have to be replaced every time there is a tear down and MOST OFTEN the owner is unwilling to pay for that or wait for an extended period for a rebuild. They just insist on me doing "WHAT EVER QUICK, MAGIC, THING YOU DID LAST TIME TO MAKE IT WORK".
I just sprayed a little slicky on it (WD-40) and yanked it back and forth.
I could do about the same thing with some paint thinner and some 10wt but hey . . . there's WD-40.
Here's another one : People berate British cars for their electrical systems. If one knows how to clean a contact now and then here and there . . . no problem.
The one and only time I ever had a problem starting my old British car was I had just washed the engine and had gotten water on the distributor cap. As the engine cooled it drew the moisture under the cap there is some pretty big areas where this can happen. Later I got in and it wouldn't fire.
I popped the distributor cap, sprayed a little WD in there and it fired first try and we were off.
Not sure what would have happened if I had used paint thinner but . . . it might have blew the cap off the distributor.